In standard computer systems, the file system (e.g., NTFS on Windows or ext3 for Linux) is responsible for keeping track of the tree or hierarchy of files. It also stores files in fixed-size blocks on the disk and keeps track of where these blocks are located. Backup applications that read files using the file system to access data are inherently slow. Block based backups (BBB) bypass files and file systems by reading directly from the disk or volume, thus they incur no performance penalty for even large numbers of files because the backup application reads blocks in their order on the disk, not the order that they appear in files. Block based backups also support point-in-time snapshots in which a backup is started by first taking a snapshot of the live running volume. They then read block level data from the snapshot not the actual disk. In general, block-based backups are many times faster for backup and restore operations, as compared to traditional file system based backup systems.
The advent of virtualization technology has led to the increased use of virtual machines as data storage targets. Virtual machine (VM) disaster recovery systems using hypervisor platforms, such as vSphere from VMware or Hyper-V from Microsoft, among others, have been developed to provide recovery from multiple disaster scenarios including total site loss. One popular backup system, such as the EMC Networker Block Based Solution creates a backup image in VHDx containers. VHDx is a Hyper-V virtual hard disk (VHD) format found in Windows servers, and has a present storage capacity of 64 TB compared to standard VHD storage limits of 2 TB. A container is an image file that stores backups.
With respect to block based backups, systems such as EMC Networker creates a volume image in a VHDx container. The VHDx container is created on a disk type device like Data Domain, DD or advance file type device, AFTD. Full backups contain either all blocks or used blocks of the volume in VHDx. Incremental backups contain changed blocks embedded in the VHDx container. For file recovery, the system mounts the VHDx chain and user can copy the required files from mounted file system. During image recovery, it recovers the blocks from all backup images (i.e., from all backup levels). Each VHDx contains the required volume to be protected and additionally a system partition if required. At the virtual hard disk layer, the system can represent a large virtual disk only up to 64 TB. This means the maximum volume size plus VHDx metadata should not go beyond 64 TB. For volumes that are greater than 64 TB, the system does not support block based backups. This represents a significant limit on the availability of block based backups and forces backup systems to revert to file level backups for large volumes.
What is needed, therefore, is a block based backup system that supports volume sizes greater than 64 TB by extending the block based backup frame work when Data Domain or similar systems is used as the backed storage device.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions. EMC, Networker, Data Domain, Data Domain Restorer, and Data Domain Boost are trademarks of EMC Corporation.